Technical Field
The present invention relates to a voltage conversion circuit for lowering an output voltage from a power supply into a voltage supplied to a load circuit, and an electronic apparatus including the same.
Related Art
Due to recent trends toward energy saving, attention has been focused on environmental energy which exists commonly and does not rely on fossil fuels and the like. Power generation energy from sunlight, wind power and the like has been widely known as such environmental energy. On the other hand, as environmental energy with an energy density not lower than that of such power generation energy, there is vibration energy existing commonly in daily life. In order to supply a load circuit with electric power from a power generation device adapted to perform power generation from such vibration energy, there has been a circuit for performing voltage conversion thereof into a supply voltage suitable for the load circuit. Therefore, conventionally, studies have been made to improve the conversion efficiency.
For example, in consideration of the difficulty in attaining desired voltage drop due to the output impedance of the vibration power generation device, there has been disclosed a technique for suppressing degradation of the voltage conversion efficiency (refer to Patent Document 1). According to the technique, there are provided switching circuits for changing over the connection states of the plurality of capacitors to a power supply circuit and to a load circuit, between serial connection and parallel connection, such that the number of capacitors connected through the switching circuits is controlled, based on the input voltage from the power supply circuit and the frequency thereof. In addition, Patent Document 2 discloses a technique for performing efficient power generation from vibration with smaller vibration amplitude. According to this technique, ON/OFF control is performed on a switch for controlling electric power outputted from a vibration power generation device, based on a period of vibration, in order to change the period of the outputted electric power.
Patent Document 1: Japanese Unexamined Patent Publication No. 2009-124807
Patent Document 2: Japanese Unexamined Patent Publication No. 2005-130624
Patent Document 3: Japanese Unexamined Patent Publication No. 2005-198453